Gated beam tube relaxation oscillator



Jan. 19, 1960 c. E. TSCHIEGG 2,922,121

GATED BEAM TUBE RELAXATION OSCILLATOR Filed March 25, 1957 A I l F ACCELERA 70R 5 V L CATHODE n m 2v aoov 6 5+ 1 9 2 9 PLATE ,1 3 7 /3 ANODE 7 QUAD.

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6 j 6 Lumemu /2 T W ACCELERATOR 5 CA'IH [4 1A I CATHODE I INVENTOR /5 farm/l 2F. Isa/212399 BY MW Y ATTORNEY M i. m AGENT United States Patent GATE!) BEAM TUBE RELAXATION OSCILLATOR Carroll E. Tschiegg, Silver Spring, Md., assignor to the United States of America as represented by the Secretar-y of Commerce Application March 25, 1957, Serial No. 648,450

2 Claims. (Cl. 331-152) This invention relates to pulse generators and more particularly is concerned with a novel relaxation oscillator generator employing a single tube of the gated beam type.

Many relaxation oscillator circuits are known to the prior art, two of the most common classes being those described as multivibrators and blocking oscillators.

The circuit of the instant invention is similar in many respects to a conventional multivibrator or a blocking oscillator but possesses the advantage of being simpler in design in that no transformer or additional tube is required for regenerative feedback.

Therefore, one object of the present invention is to provide an inexpensive pulse generator.

Another object of this invention is to provide a simple relaxation oscillator requiring only a single tube for operation.

Still another object of the present invention is to provide an improved pulse generator having a high pulse repetition frequency and a fast pulse rise time.

An additional object of this invention is to provide an improved pulse generator the operation of which is independent of external loads.

Other uses and advantages of the invention will become apparent upon reference to the specification and drawings, of which-- Fig. 1 is a circuit diagram of a free running form of the novel relaxation oscillator of the present invention;

Fig. 1A is a more detailed view showing the internal construction of a 6BN6 type gated beam tube;

Fig. 2 is a diagram of the waveform appearing at the various electrodes of the tube shown in the circuit of Fig. 1.

Referring to the drawings, in Fig. l is shown a circuit diagram of a free running embodiment of the relaxation oscillator of the present invention. The oscillator comprises a gated beam tube 3 having a plate electrode 7, a quadrature grid 2, an accelerator electrode 5, a limited grid 6, and a cathode 1. The internal structure and operation of such a tube is well known and is described, for example, in the technical section of the Sylvania News, vol. 23, No. 4, 1956, pp. 58.

A positive feedback path from the accelerator electrode 5 to the limiter grid 6 is provided by capacitor 12. Resister 8 is a plate load resistor and resistor 143 is a cathode load resistor. Resistor 10 can be eliminated in the free running circuit if the output is taken from the plate by way of lead 13. Resistor 11 is a biasing resistor for the limiter grid 6. Also shown is an accelerator load resistor 9.

Output terminals 13 and are provided for deriving an output signal from the plate of tube 3 while terminal 14 in conjunction with terminal 15 provides for a cathode output signal. If desired, terminal 14 may serve as a means for applying a negative cathode triggering pulse to the circuit.

Fig. 1A is a more detailed view of the internal construction of a 6BN6 gated beam tube of the above-identified type. The various electrodes identified in Fig. l are 2,922,121 Patented Jan. 19, 1960 correspondingly labeled in Fig. 1A. Fig. 1A particularly emphasizes the relation of the accelerator grid 5 to the limiter 6 and cathode 1 of the tube. Such specific construction is significant in explaining the operation of the present invention as an oscillator. Specifically, the accelerator current normally reaches only the accelerator grid 5 when the limiter grid 6 is negative and no portion of the accelerator current therefore can reach the anode 7. When the limiter 6 is driven above cut-oft as will be described, then the accelerator current is switched over to the anode 7.

Because of the described arrangement and shape of the electrodes in the gated beam tube 3, either of the two control grids 2 or 6 can cause complete plate current cutofi regardless of the potential on the other grid. Furthermore, the cathode current does not depend upon the potential of the grids 2 and 6 but rather on the potential of the accelerator 5. Thus it is possible to self-bias the tube to plate current cutofi with a resistor 10 in the cathode circuit. The grids 2 and 6 act as gates which switch a portion of the accelerator current to the plate, the cathode current remaining essentially constant. This self-bias feature plus an elfective second control grid 2 (for high impedance trigger) makes this tube well suited for triggered oscillator application;

The mode of operation of the circuit in Fig. 1 can be explained in the following manner. Assume the plate current is cut olf by a negative potential on the limiter grid 6. As the grid bias network of resistor 11 and capacitor 12 recharges, the circuit will remain quiescent until the cutoff value for limiter grid 6 is reached. At this point, that is, when the limiter 6 goes above cut-off a portion of accelerator current which in this type of tube as above described normally is limited to accelerator grid 5, is switched to the plate. This causes the potential of the accelerator grid 5 to rise and that of the plate 7 to fall. The current transfer is regenerative; as the accelerator potential rises it is fed back in phase through the feedback path provided by capacitor 12 to the limiter grid 6 and the resulting increase in limiter grid voltage makes the switch more rapid. As the accelerator grid 5 becomes more positive it begins to draw grid current until capacitor 12 develops a negative cutoff bias. Because of this negative bias on limiter grid 6 the plate current is then regeneratively switched back to the accelerator 5 and the cycle is completed.

The waveforms in Fig. 2, showing the voltage wave appearing at the cosrrespondingly numbered electrodes of the tube of Fig. 1 over three complete cycles of operation, illustrate the above action.

Specifically, it will be clear that when the limiter grid 6 is at cut-off, there will be no output from plate 7. Also the circuit remains quiescent until the limiter grid is biased beyond cut-off as shown by the fiat portions be tween the output pulses and the waveform for plate'7 shown in Fig. 2.

The potential on limiter grid 6 is shown below the waveform of plate 7 in Fig. 2. As indicated by the waveform for limiter grid 6, as capacitor 12 charges, the limiter grid will be driven above cut-oil. Due to the consequent switching action, the accelerator current will be switched to the plate as described.

At such point, as indicated by the line L1 in Fig. 2, the potential of the anode 7 drops. As indicated by the waveform for limiter grid 6 in Fig. 2, the limiter grid is then driven to cut-01f (line t2 in Fig. 2) causing the plate current to be switched back to accelerator grid 2 and restoring the potential at anode 7. The above action results in a repetition pulse output as is represented by waveform 7 in Fig. 7.

The pulse widths shown in Fig. 2 are about three microseconds at a pulse repetition frequency of 20 kc. Pulse rise and decay times are about 0.1 microsecond for the plate and about 0.04 microsecond for the cathode pulses.

The free-running pulse repetition frequency (or recovery time When triggered) 'is proportional to the time constant of resistor 11 and capacitor 12; The'pulse width is determined by capacitor 12 a'ndthe internal impedance of the limiter grid 6. The plate load resistor, 8 can he increased for greater output;'however, this procedure increases the rise and decay times. Cathode resistor 10 should be increased from 270 ohms to 560 ohms for triggered operation.

The economy and versatility of the gated beam tube relaxation oscillator ofthe present invention makes it a useful addition to existing pulse circuitry. Several obvious modifications are possible which include the use of inductive plate loads or tuned circuits in the feedback path. A series resonant crystal can also be used provided some means for limiting the crystal current is included. The pulse repetition frequency Will then be synchronized at the fundamental or some sub-harmonic of the crystal frequency depending upon the time constant of resistor 11 and capacitor 12.- A tuned circuit can be used in the output it a sinusoidal Waveform is desired.

It will be apparent that the embodiment shown is only exemplary and that various modifications can be made in construction and arrangement Within the scope of the invention as defined in the appended claims.

What is claimed is:

1. A pulse generator for producing an asymmetrical waveform comprising a gated beam tube of the 6BN6 type having a cathode and anode for generating an electron beam and a plurality of grids mounted in the path of said'beam between said cathode and anode including a first limiter control grid and a second quadrature control grid adjacent said cathode and anode respectively and an accelerator grid mounted. between said tWo control grids, a potential source having positive and negative terminals, separator resistor means connecting the positive terminal of said potential source to said anode and accelerator grid respectively, a feedback capacitor connecting said accelerator grid to said limiter grid, means connecting said quadrature grid to said cathode, a resistor connecting the cathode to the negative terminal of said potential source, and a resistor connecting said limiter grid to the negative side of said potential source.

2. The invention of claim 1 including means for applying an external trigger signal to said cathode and quadrature grid.

References Cited in the file of this patent FOREIGN PATENTS Australia June 19, 1941 Great Britain Sept. 16, 1953 OTHER REFERENCES 

